Assessment of surface/subsurface damage in early-stage fatigue: A new attempt based on LCR wave

Abstract

To facilitate a surface/subsurface fatigue damage awareness in the early stage, a signal-steady, thickness-independent, nondestructive method is proposed based on a critically refracted longitudinal (LCR) wave, which is compared with the conventional pulse-echo ultrasonic technique. With the evolution of cyclic damage in microscale, a normalized amplitude difference of LCR wave,Adif, increases monotonically, but the attenuation coefficient of the pulse-echo method evolves non-monotonically. The effects of surface roughness on the propagation of LCR wave are studied. A discrete strategy is proposed to detach the coupling between surface roughness and dislocation damping, and the mechanism is discussed with dislocation density-based calculation.